Mast cells play key roles in allergic reactions and in a number of inflammatory disorders. Following activation, mast cells release a variety of cytokines as well as histamine, proteoglycans, and lipid-derived mediators (Stevens and Austen, 1989, Immunol. Today 10:381-386; Corrigan and Kay, 1991, Am. Rev. Respir. Dis. 143:1165-1168). Tryptase and chymase, serine proteases with trypsin-like and chymotrypsin-like substrate specificities respectively, represent the major protein constituents of human mast cells and are also released upon activation (Schwartz et al., 1981, J. Biol. Chem. 256:11939-43; Schwartz et al., 1987, J. Immunol. 138:2611-2615; Smith et al., 1984, J. Biol. Chem. 259:11046-51; and Schechter et al., 1983, J. Biol. Chem. 258:2973-2978). Serine proteases such as chymases and tryptases generally require post-translational removal of N-terminal amino acids (prepro sequences) to become proteolytically active (Birch and Loh, 1989, in "Proteolytic Enzymes: a practical approach," Beynon and Bond, eds., IRL Press: Oxford, pp. 211-230). Chymase is found in only a subset of human mast cells, unlike tryptase, which is found in all human mast cells (Irani et al., 1986, Proc. Natl. Acad. Sci. U.S.A. 83:4464-4468). The role of these proteases in the allergic and inflammatory responses mediated by mast cells is not well understood. However, a number of studies suggest that these enzymes may contribute to the pathophysiology of airway disease states such as asthma and cystic fibrosis (Tam and Caughey, 1990, Am. J. Respir. Cell Mol. Biol. 3:27-32; Tam et al., 1989, Am. Rev. Respir. Dis. 139:A200; Ollerenshaw et al., 1989, N. Engl. J. Med. 320:1244-1248). Chymase, for example, is an extremely potent secretagogue for airway submucosal gland cells, suggesting a potential role for this enzyme in the abnormal mucus secretion characteristic of asthma (Sommerhoff et al., 1989, J. Immunol. 142:2450-2456).
As a first step towards understanding the role of chymase in human airway disease, a reliable source of recombinant human chymase is required to facilitate structure/function and inhibitor studies of this enzyme. Genomic DNA sequences encoding human chymase have recently been cloned; the deduced placental cDNA sequence (Caughey et al., 1991, J. Biol. Chem. 266:12956-63) is identical to the cloned heart cDNA sequence (Urata et al., 1991, J. Biol. Chem. 266:17173-79). Expression of recombinant dog chymase as a fusion protein has been disclosed, although processing of the fusion protein to form mature dog chymase was not reported (Rani et al., 1992, FASEB J. 6:A1346).
Thus there is a need in the art for reliable recombinant expression of a functionally active chymase. Moreover, there is a need in the art for recombinant expression of a chymase or derivative thereof comprising a proteolytically active chymase catalytic domain.
Citation of references hereinabove shall not be construed as an admission that such is prior art to the present invention.